Relapse of the underlying malignancy is the most common cause of treatment failure following autologous marrow transplantation and remains a significant problem following allogeneic transplantation. A variety of approaches are under active investigation to reduce relapse rates. In this project we will study an unique population of ex-vivo expanded T cells which co-express the NK cell marker CD56. These expanded cells, which we have termed cytokine induced killer (CIK) cells have potent anti-tumor cell activity both in vitro and in vivo as demonstrated in SCID mice engrafted with human lymphoma cells. The cell surface phenotype of the cells with the greatest lytic activity is CD3+CD56+CD16-. These cells which are derived from T cell and not NK cell percursors expand maximally 1,000 fold under the culture conditions that we have developed. These include pretreatment with interferon-gamma followed one day later with anti-CD3 MAb, IL-2 and IL-1. It is our hypothesis that CIK cell based immunotherapy will prove to be an effective treatment approach to reduce relapse rates and will allow us to treat patients who have suffered a relapse following transplantation. In this project we will focus on three critical biological questions which have basic as well as clinical significance. Firstly, we will identify the role of accessory cells, co-stimulatory signals and cytokines in the ex-vivo expansion of CIK cells. Secondly, we will compare the mechanisms of tumor cell and endothelial cell recognition and cytotoxicity since we have previously identified major differences in the mechanism by which these disparate target cells are killed. These observations could help reduce the toxicity associated with cellular immunotherapy. Thirdly, we will utilize the SCID/hu lymphoma model system that we have developed as well as a recently developed SCID/hu leukemia model to study and optimize the in vivo activity of ex-vivo expanded autologous CIK cells and cells from HLA-matched donors. This model system will be used to potentially optimize the in vivo efficacy of CIK cell based immunotherapy as well as identify the cellular populations which are most effective. We believe that through these studies basic observations on the mechanisms of cell expansion and cell-cell recognition will be gained as well as insights which will hopefully result in less toxic and more effective forms of immunotherapy. The clinical application of CIK cell based immunotherapy will be explored in other subprojects.